Tapering a tentacle mesh with uniformly scaled suction discs
Duplication on Faces

Consider Proportional Editing manually or by modifier.  Curve guide with [no] radius adjustment.



Above Detail view. Blue Tentacle Curved Form Tapered.  Discs Not Tapered. I used a semi torus as a disc for this discussion. 



Above the Duplication Settings for the tentacle highlighted above. Scaling is uniform for this feature.  No ellipse forms are introduced.  This feature renders duplicates and does [not] render the two original meshes.  Surprising but useful.  For the question above you need one mesh for visual rendering and one for placement of duplicated discs.  Total 2 Meshes for final render.  One mesh visible. One not visible.  



The disc is parented to the other mesh, this is a requirement .



Above larger view.  Curve Highlighted.  Second set of Discs not placed on any other mesh.  This is just to show versatility of placement.  Original straight Cylinder form with no modifiers.  The two gray cubes used as the tapering objects for a Warp Modifier. I used the warp modifier, as one option, because I wanted visual interaction. You need [not] use the warp modifier. You may [proportional edit] by hand.  You may also use [shape keys].



Above show 2 (two) blue tapered meshes.  The highlighted blue mesh has the curve modifier disabled so we can see both blue meshes easily. The highlighted mesh was copied from the other and then Duplication on Faces was turned off. One blue mesh is rendered and has [no] duplication on faces.  The other other blue mesh is for placement of discs and is not rendered.  This separation of placement and render is a feature.  It is highly likely you need to use 2 meshes in the same fashion.



Above rendered image showing custom placement of discs by deletion of faces, not vertices, of the duplicator.  The viewable mesh was not changed.  2 Meshes are used as stated above.



Above the deleted faces of duplicator.



Above rendered image smoothed and using subdivision surface modifier.

Secondary

You can consider [Make Duplicates Real] on the duplicator to create multiple meshes and turning off face duplication on the duplicator.